Use Of Antenna Factors In EMI Measurements

By Com-Power Corporation

There are various technical parameters associated with antennas which are commonly studied and defined; including gain, directivity, beamwidth (or beam area), aperture, antenna pattern, antenna temperature, and antenna radiation resistance. The antenna factor is rarely included as one of the basic parameters of an antenna, as it is used almost exclusively in EMI testing when making radiated electric field strength (E-field) measurements. E-field measurements are necessary for determining compliance with most electromagnetic interference requirements/standards, such as FCC Part 15, CISPR 22, EN 55022, etc. Many engineers starting new in the EMC field may find the concept of antenna factor and its explanation useful.

This application note defines the antenna factor and explains how this concept simplifies the measurement of E-field using an EMC antenna. Also included in this discussion are the basic parameters of other measurement system components typically used along with the antenna for making E-field measurements. Finally, some practical limitations of this concept are discussed along with precautions to be taken.